Emergency signal system for vehicles

ABSTRACT

A vehicle signaling system for alerting drivers approaching from a rear of a vehicle is provided which includes an audio signal emitting device, preferably arranged on the vehicle facing rearward, having an activated state in which an audio signal is emitted and an inactivated state in which an audio signal is not emitted. The system also includes velocity measurement means for measuring an absolute velocity of the vehicle, deceleration measurement means for measuring deceleration of the vehicle, the deceleration measurement means being operatively associated with the brake pedal of the vehicle such that deceleration of the vehicle is measured by the deceleration measurement means after the brake pedal is depressed, and control means coupled to the velocity measurement means and the deceleration measurement means for activating the audio signal emitting device from its inactivated state to its activated state only if the absolute velocity is greater than a threshold velocity in the control means and the measured deceleration is greater than a deceleration threshold in the control means. The system also includes means for enabling manual activation of the audio signal emitting device from the inactivated state to the activate state when the measured absolute velocity is less than a threshold velocity.

FIELD OF THE INVENTION

[0001] The present invention relates generally to a vehicular emergencystopping signal system and, in particular, to an emergency stoppingsignal system which is intended to prevent rear-end collisions byalerting drivers that the automobile traveling in front of them isstopped or decelerating rapidly via audio signals.

BACKGROUND OF THE INVENTION

[0002] At the present time, a serious problem exists with currentvehicular braking or stopping signal systems. In particular, currentsignal systems are limited to light signals. Such light signal systemstypically consist of brake lights that are activated by applying orpumping the brake pedal. Alternatively, light signal systems consist ofred hazard flashers, which are activated manually by the driver.

[0003] Such light signal systems have several drawbacks. For example,such systems do not alert drivers who are not looking directly ahead ofsuddenly stopping or decelerating vehicles. A driver who is adjustinghis or her radio or other instrument on the vehicle's dashboard, or whois simply not paying direct attention to the vehicle traveling ahead, isnot alerted to a stopping or decelerating vehicle by a light signalsystem.

[0004] Moreover, light signal systems do not alert drivers to suddendecelerations when traveling at high velocities. Usually, when travelingat high velocities, such as on freeways, sudden deceleration of avehicle is not adequately conveyed to drivers behind the vehicle bymeans of the usual brake lights on a vehicle. Rather, the drivers in thevehicles behind the decelerating vehicle may view the illumination ofthe brake lights as a small reduction in speed, which would beinterpreted as not requiring a concomitant braking, as opposed to alarge reduction in speed, which is obtained by a sudden deceleration andwould require braking.

[0005] Systems have been developed which attempt to remedy the latterdrawback discussed above. Specifically, applicants' own U.S. Pat. No.5,786,752, the complete disclosure of which is incorporated herein byreference, discloses a signaling system for alerting drivers approachingfrom the rear of a vehicle which includes one or more novel lightsignals activated only when the vehicle traveling ahead is traveling ata velocity above a predetermined threshold velocity and when the vehicletraveling ahead is decelerating at a rate above a predeterminedthreshold deceleration. At any other conditions, the light signal(s)will not be activated. Thus, the activation of the novel light signal(s)will unequivocally alert drivers that the vehicle is deceleratingrapidly and thus those drivers must also decelerate in order to avoidaccidents. In this manner, a fully automatic emergency signal system isprovided without a large potential for error, i.e., false indications ofsudden deceleration, since there must be some affirmative action by thedriver, i.e., applying pressure to the brake pedal, to activate thesignal system in accordance with the invention, provided the vehicle istraveling above a certain velocity.

[0006] However, no attempts have been made at remedying the formerdrawback. Specifically, there exist no systems for alerting drivers ofsuddenly stopping or decelerating vehicles who are not looking ahead atthose vehicles.

OBJECTS AND SUMMARY OF THE INVENTION

[0007] It is therefore an object of the present invention to avoid theabove drawbacks of the current signal systems.

[0008] It is another object of the present invention to provide methodsand devices for creating a novel and prominent signal system forvehicles such as automobiles that will help prevent rear end collisionsby rapidly and decisively alerting drivers approaching from the rearthat the vehicle ahead is rapidly decelerating.

[0009] It is yet another object of the present invention to provide anew and improved emergency signal method and system for alerting driverswho are not looking ahead of suddenly stopping, stopped, or deceleratingvehicles.

[0010] To achieve these objects, and others, a vehicle signaling systemfor alerting drivers approaching from a rear of a vehicle is providedwhich includes an audio signal emitting device, preferably arranged onthe vehicle facing rearward, having an activated state in which an audiosignal is emitted and an inactivated state in which an audio signal isnot emitted. The system also includes velocity measurement means formeasuring an absolute velocity of the vehicle, deceleration measurementmeans for measuring deceleration of the vehicle, the decelerationmeasurement means being operatively associated with the brake pedal ofthe vehicle such that deceleration of the vehicle is measured by thedeceleration measurement means after the brake pedal is depressed, andcontrol means coupled to the velocity measurement means and thedeceleration measurement means for activating the audio signal emittingdevice from its inactivated state to its activated state only if theabsolute velocity is greater than a threshold velocity in the controlmeans and the measured deceleration is greater than a decelerationthreshold in the control means.

[0011] The control means includes velocity threshold determining meanscoupled to the velocity measurement means for determining if themeasured absolute velocity is greater than the threshold velocity. Inaddition, the control means includes deceleration threshold determiningmeans coupled to the deceleration measurement means for determining ifthe measured deceleration is greater than the threshold deceleration.The velocity sensor includes, without limitation, a sensor operativelyconnected to the speedometer, engine, or transmission drive train, anair velocity or air pressure sensor to measure the relative velocity ofoutside airflow with respect to the vehicle, or a software subroutine inthe vehicle's computer to calculate the vehicle's instantaneousvelocity. The deceleration measurement means includes, withoutlimitation, a velocity sensor coupled to the brake pedal for measuringthe velocity with which the brake pedal is depressed, a decelerationmeasurement sensor connected to the brake pedal, a sensor coupled to thebrake pedal for sensing the force applied to the brake pedal, a softwaresubroutine in the vehicle's computer for calculating the vehicle'sinstantaneous deceleration, or an accelerometer.

[0012] The audio signal emitting device includes current automobile andvehicle horns as well as audio signal generating devices that producenovel audio signals. The audio signals would be directed substantially,though not necessarily exclusively, rearward so as to be audible toother vehicles approaching from behind the vehicle. The audio signalwould be of sufficiently high level to be heard by drivers behind thevehicle at a reasonable distance in which to respond to the change invehicle velocity. In one embodiment, the audio signal emitting devicewould be a unique, standardized horn sound that is directedsubstantially rearward from the vehicle. In another embodiment, theaudio signal emitting device produces a unique loud sound or a series ofnovel horn sounds, or any sound that would grab the attention of thedriver behind, such as a Morse code signal. The audio signal emittingdevice could be built into the rear of the vehicle's body or the rearbumper, or mounted on the undercarriage facing rearward. The decibellevel of such an audio signal emitting device would be sufficiently loudso that drivers behind would be alerted quickly at a safe distance. Theaudio signal emitting device could be a compressed air horn orelectromechanical horn.

[0013] In another embodiment of the invention, a vehicle signalingdevice for alerting drivers approaching from a rear of the vehicle isprovided which includes an audio signal emitting device arranged on thevehicle having an activated state in which an audio signal is emittedand an inactivated state in which an audio signal is not emitted. Thedevice includes means for enabling manual activation of the audio signalemitting device from the inactivated state to the activated state,velocity measurement means for measuring an absolute velocity of thevehicle, and control means coupled to the velocity measurement means andthe manual activation enabling means. The control means enableactivation of the audio signal emitting device from the inactivatedstate to the activated state by the manual activation enabling means ifthe measured absolute velocity is less than a threshold velocity.

[0014] In another embodiment of the invention, a vehicle signalingdevice for alerting drivers approaching from a rear of the vehicle isprovided which includes an audio signal emitting device arranged on thevehicle having an activated state in which an audio signal is emittedand an inactivated state in which an audio signal is not emitted. Thedevice includes means for enabling activation of the audio signalemitting device from the inactivated state to the activated state,velocity measurement means for measuring an absolute velocity of thevehicle, deceleration measurement means for measuring deceleration ofthe vehicle, and control means coupled to the deceleration measurementmeans and the velocity measurement means. The control means is coupledto the deceleration measurement means and is arranged to activate theaudio signal emitting device from its inactivated state to its activatedstate if the absolute velocity is greater than the threshold velocity inthe control means and the measured deceleration is greater than adeceleration threshold in the control means.

[0015] In another embodiment of the invention, a method for alertingdrivers approaching from a rear of the vehicle to changes in thevelocity of the vehicle is provided which includes the steps ofarranging on the vehicle an audio signal emitting device having aninactivated state and an activated state in which an audio signal isemitted and controlling the activation of the audio signal emittingdevice in relation to the rate of change of velocity of the vehicle. Theactivation controlling step includes the steps of measuring an absolutevelocity of the vehicle, measuring deceleration of the vehicle after abrake pedal of the vehicle is depressed, and activating the audio signalemitting device from its inactivated state to its activated state onlyif the absolute velocity is greater than a threshold velocity and themeasured deceleration is greater than a deceleration threshold.

[0016] In another embodiment of the invention, a method for alertingdrivers approaching from a rear of the vehicle to changes in thevelocity of the vehicle is provided which includes the steps ofarranging on the vehicle an audio signal emitting device having aninactivated state and an activated state in which an audio signal isemitted and controlling the activation of the audio signal emittingdevice in relation to the absolute velocity of the vehicle. Theactivation control step includes the steps of measuring an absolutevelocity of the vehicle and enabling manual activation of the audiosignal emitting device from the inactivated state to the activated stateif the measured absolute velocity is less than a threshold velocity.

[0017] In another embodiment of the invention, a method for alertingdrivers approaching from a rear of the vehicle to changes in thevelocity of the vehicle is provided which includes the steps ofarranging on the vehicle an audio signal emitting device having aninactivated state and an activated state in which an audio signal isemitted and controlling the activation of the audio signal emittingdevice in relation to the absolute velocity of the vehicle and thedeceleration of the vehicle. The activation control step includes thesteps of measuring an absolute velocity of the vehicle, measuringdeceleration of the vehicle, and automatically activating the audiosignal emitting device from its inactivated state to its activated stateif the absolute velocity is greater than a threshold velocity and themeasured deceleration is greater than a deceleration threshold.

[0018] These embodiments of the present invention solve the problem withcurrent light signal systems, namely, alerting drivers who are notlooking directly ahead of sudden decelerations of vehicles at highvelocities. Specifically, a novel signaling device for alerting driversapproaching from a rear of the vehicle is provided which includes one ormore audio signal emitting devices. The audio signals are activatedautomatically only when a vehicle is traveling at a velocity above apredetermined velocity, i.e., the threshold velocity, and the vehicle'sdeceleration, is above a predetermined deceleration, i.e., the thresholddeceleration. The audio signal may also be activated manually when themeasured velocity is below a threshold velocity. At any otherconditions, the audio signal emitting device(s) will not be activated.

[0019] Thus, the activation of the audio signal emitting device(s) willunequivocally alert drivers, who may not be looking directly at thevehicle traveling ahead, that the vehicle is decelerating rapidly orstopped and that he or she must also decelerate in order to avoidaccidents.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The following drawings are illustrative of embodiments of theinvention and are not meant to limit the scope of the invention asencompassed by the claims.

[0021]FIG. 1 is a side view of a vehicle having a rear-mounted audiosignal emitting device in accordance with the invention.

[0022]FIG. 2 is a rear perspective view of a vehicle having a standardthree brake light system in which all three lights are simultaneouslyilluminated.

[0023]FIG. 3 is a schematic diagram of a sensing and control system forthe audio signal emitting device systems in accordance with theinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Referring to the accompanying drawings wherein the same referencenumerals refer to the same or similar elements, in the embodiment ofFIG. 1, an audio signal emitting device 12 is positioned on a rearelement 16 of the vehicle 10, e.g., on the trunk or rear panel. Theaudio signal emitting device emits sound waves 14. Such sounds may be inthe form of several types of sounds, including but not limited to,automobile horns or truck horn sounds, siren wails, human voices orother sounds. The types of sounds may be varied in presentation so thata series of loud horns could be followed by a loud siren wail. Soundscould be presented in a rapid series, such as a series of loud buzzes.Sound types could be intermixed. For example it is known that lowfrequency sounds carry farther than high frequency sounds and an audiosignal could be comprised of low frequency sounds to preferentiallyalert drivers who are further behind, alternating with higher frequencysounds to preferentially alert drivers who are closer. Soundstraditionally associated with emergency stops such as a siren would beeffective in grabbing the attention of the driver behind. Constantsounds of a continuous repeated nature, such as a single frequency,could be used since oncoming drivers would hear a Doppler shift infrequency as the relative velocity of the two vehicles changed duringthe deceleration of the car ahead. This Doppler shift would enhance therecognition of any rearward directed audio signal.

[0025] Audio signaling devices could be mounted on the rear bumper,incorporated into the chassis or body of the vehicle, or mounted on theundercarriage. Electromechanical horns or compressed air could beutilized. Compressed air horns could incorporate a visible gas componentto enhance alerting the driver behind.

[0026] The audio signal emitting devices are connected to an actuationsystem such as described below with reference to FIG. 3.

[0027]FIG. 2 shows a prior art braking system on a vehicle. The systemincludes three brake lights 202,204,206, two lights 202,204 on a rearpanel 208 of the vehicle 200 and a third 206 in a central location abovethe trunk, and often within the vehicle interior compartment. As isconventional in the art, all three of these lights 202,204,206illuminate at a standard illumination simultaneously upon depressing thebrake pedal, regardless of the intensity of the force exerted on thebrake pedal.

[0028] In accordance with each embodiment of the invention, a sensingand control system is coupled to the audio signal emitting devices. Thesensing and control system or actuation means activates or preventsactivation of the audio signal emitting devices. One embodiment of asensing and control system is illustrated in FIG. 3 and comprisesvelocity measurement means such as a velocity sensor 110 connected to aspeedometer 112 in the automobile, or alternatively to an integratingaccelerometer 114, which senses and records the automobile's absolutevelocity. When the absolute velocity of the automobile is sensed to bebelow a set threshold as determined by suitable determining/comparisonmeans such as threshold detector 116 into which the set threshold isentered, a relay 118, which is coupled to the threshold detector 116 andnormally closed, is de-energized thereby enabling manual switch 120 toactivate an audio signal through an “or” gate 122.

[0029] Other means for enabling manual activation of the audio signalemitting device 124 on condition that the measured velocity is greaterthan the threshold velocity as determined by the threshold detector 116can be used without deviating from the scope of the invention. Thethreshold detector 116, the relay 118, switch 120 and “or” gate 122constitute parts of a control unit or control means for the audio signal124. If the velocity of the automobile is above the threshold velocity,relay 118 is energized and the relay contacts become opened therebypreventing switch 120 from activating the audio signal emitting device124 through the “or” gate 122, i.e., activation of switch 120 will notactivate the audio signal emitting device 124. In this manner, the audiosignal is prevented from being manually activated while the car istraveling at normal highway speeds. Such a feature prevents activationof the audio signal emitting device inadvertently or by intentionalabuse of the warning system. If the car were to be stopped in traffic ortraveling below the threshold speed, then relay 118 would bede-energized thereby enabling switch 120. The threshold speed could beselected to be an abnormal and unsafe low speed for highway, freeway andstate and federal road driving. Upon enabling of switch 120, the audiosignal emitting device 124 could then be activated manually by thedriver of the vehicle to alert drivers approaching from the rear thatthe car is stopped or stopping in a traffic lane. It is understood that,in the same manner that audio signal emitting device 124 is activated, aplurality of such audio signal emitting devices could be activatedsimultaneously or sequentially to thereby achieve the objects of theinvention. For example, the “or” gate could lead to several audio signalemitting devices 124 to provide for intermittent emission of a pluralityof audio signals coupled thereto, e.g., in a sequential arrangement.

[0030]FIG. 3 also shows a second sensing and control system inaccordance with the invention that can be used together with, orindependent of, the sensing and control system described above. In thissecond sensing and control system, a relay 126, which is normally open,is controlled by the output of the threshold detector 116. If thevehicle is traveling above the threshold velocity, then relay 126 isalso energized. This permits activation of sensor 128, i.e., the relay126 constitutes a sensor activation mechanism. Sensor 128 may be ofseveral types of detectors, which measure deceleration of the car. Forexample, sensor 128 may be a decelerometer, which measures theautomobile's deceleration. Once the deceleration exceeds a certainthreshold value as detected by a deceleration threshold determining unit132 coupled to the deceleration measurement sensor 128, a signal is sentthrough wire 130 to the “or” gate 122 thereby activating the audiosignal emitting device 124. As such, activation of the audio signalemitting device 124 is based on the measured velocity of the vehiclebeing greater than a velocity threshold and the deceleration of thevehicle being greater than a deceleration threshold. Also, in theembodiment wherein both sensing and control systems are operating, thereare two ways in which the audio signal emitting device 124 can beactivated, either manually when the measured velocity is less than thethreshold velocity or automatically when the measured velocity isgreater than the threshold velocity and the deceleration of the vehicleis greater than a deceleration threshold.

[0031] Deceleration measurement sensor 128 may be a strain gauge,pressure sensor, or velocity sensor operatively connected to the brakepedal thereby sensing the force and/or velocity with which the brakepedal is depressed. Strong pressure applied for a minimum, defined timeinterval on the brake pedal would correlate with a rapid decelerationand subsequently result in a signal being transmitted through wire 130to actuate the “or” gate 122 and subsequently the audio signal emittingdevice 124. If the vehicle is traveling below the threshold velocity,relay 126 is de-energized thereby preventing activation of sensor 128based on the deceleration of the vehicle. This prevents inadvertentactivation of the audio signal generating means 124 at low speeds belowthe threshold speed or when stopped, such as when one applies pressureto the brake while stopped at a red light, based on a rapid decelerationor braking action.

[0032] The examples provided above are not meant to be exclusive. Manyother variations of the present invention would be obvious to thoseskilled in the art, and are contemplated to be within the scope of theappended claims. For example, methods for alerting drivers approachingfrom a rear of the vehicle to changes in the velocity or rate of changein the velocity, e.g., deceleration, are contemplated. One such methodcomprises the steps of arranging on the rear of the vehicle an audiosignal emitting device having an inactivated state and an activatedstate in which an audio signal is emitted and controlling the activationof the audio signal emitting device in relation to the rate of change ofvelocity of the vehicle. The activation controlling step includes thesteps of measuring an absolute velocity of the vehicle, measuringdeceleration of the vehicle after a brake pedal of the vehicle isdepressed, and activating the audio signal emitting device from itsinactivated state to its activated state only if the absolute velocityis greater than a threshold velocity and the measured deceleration isgreater than a deceleration threshold.

[0033] Another method for alerting drivers approaching from a rear ofthe vehicle to changes in the velocity of the vehicle is provided whichincludes the steps of arranging on the rear of the vehicle an audiosignal emitting device having an inactivated state and an activatedstate in which an audio signal is emitted and controlling the activationof the audio signal emitting device in relation to the absolute velocityof the vehicle and the deceleration of the vehicle. The activationcontrol step includes the steps of measuring an absolute velocity of thevehicle, measuring deceleration of the vehicle, enabling manualactivation of the audio signal emitting device from the inactivatedstate to the activated state if the measured absolute velocity is lessthan a threshold velocity, and automatically activating the audio signalemitting device from its inactivated state to its activated state if theabsolute velocity is greater than the threshold velocity and themeasured deceleration is greater than a deceleration threshold.

We claim:
 1. A vehicle signaling device for alerting drivers approachingfrom a rear of the vehicle, the vehicle including a brake pedal,comprising at least one audio signal emitting device arranged on thevehicle having an activated state in which an audio signal is emittedand an inactivated state in which an audio signal is not emitted,velocity measurement means for measuring an absolute velocity of thevehicle, deceleration measurement means for measuring deceleration ofthe vehicle, said deceleration measurement means being operativelyassociated with the brake pedal of the vehicle such that deceleration ofthe vehicle is measured by said deceleration measurement means after thebrake pedal is depressed, and control means coupled to said velocitymeasurement means and said deceleration measurement means for activatingsaid at least one audio signal emitting device from its inactivatedstate to its activated state only if the absolute velocity is greaterthan a threshold velocity in said control means and the measureddeceleration is greater than a deceleration threshold in said controlmeans.
 2. The device of claim 1, wherein said control means comprisevelocity threshold determining means coupled to said velocitymeasurement means for determining if the measured velocity is greaterthan the threshold velocity, and deceleration threshold determiningmeans coupled to said deceleration measurement means for determining ifthe measured deceleration is greater than the threshold deceleration. 3.The device of claim 1, wherein said deceleration measurement meanscomprises a velocity sensor coupled to the brake pedal for measuring thevelocity with which the brake pedal is depressed.
 4. The device of claim1, wherein said deceleration measurement means comprises a decelerationmeasurement sensor connected to the brake pedal.
 5. The device of claim1, wherein said deceleration measurement means comprises a sensorcoupled to the brake pedal for sensing the force applied to the brakepedal.
 6. The device of claim 1, wherein said vehicle further comprisesa computer and wherein said deceleration measurement means comprises asoftware subroutine in the computer.
 7. The device of claim 1, whereinsaid deceleration measurement means comprises an accelerometer.
 8. Thedevice of claim 1, wherein said vehicle further comprises a speedometer,engine and transmission drive train and wherein said velocity sensorcomprises a sensor operatively connected to one of either thespeedometer, engine or transmission drive train of the vehicle.
 9. Thedevice of claim 1, wherein said velocity sensor comprises one of eitheran air velocity sensor or air pressure sensor which measures thevelocity of the airflow outside of the vehicle relative to the vehicle.10. The device of claim 1, wherein said vehicle further comprises acomputer and wherein said velocity sensor comprises a softwaresubroutine located in the computer of the vehicle which calculates thevehicle's instantaneous velocity.
 11. The device of claim 1, whereinsaid audio signal comprises a vehicle horn.
 12. The device of claim 1,wherein said audio signal comprises a siren.
 13. The device of claim 1,wherein said audio signal comprises a human voice.
 14. The device ofclaim 1, wherein said audio signal comprises a series of loud buzzes.15. The device of claim 1, wherein said audio signal comprises lowfrequency sounds alternating with higher frequency sounds.
 16. Thedevice of claim 1, wherein said audio signal comprises compressed air.17. The device of claim 1, wherein said audio signal comprises arepeating sound of a single frequency.
 18. The device of claim 1,wherein said vehicle comprises a rear bumper and wherein said audiosignal emitting device is arranged on the rear bumper of the vehicle.19. The device of claim 1, wherein said audio signal emitting device isincorporated into the chassis or body of the vehicle.
 20. The device ofclaim 1, wherein said audio signal emitting device is mounted on theundercarriage of the vehicle.
 21. A vehicle signaling device foralerting drivers approaching from a rear of the vehicle, comprising atleast one audio signal emitting device arranged on the vehicle having anactivated state in which an audio signal is emitted and an inactivatedstate in which an audio signal is not emitted, means for enabling manualactivation of said at least one audio signal emitting device from saidinactivated state to said activated state, velocity measurement meansfor measuring an absolute velocity of the vehicle, and control meanscoupled to said velocity measurement means and said manual activationenabling means for enabling activation of said at least one audio signalemitting device from said inactivated state to said activated state bysaid manual activation enabling means if the measured absolute velocityis less than a threshold velocity in said control means.
 22. A methodfor alerting drivers approaching from a rear of the vehicle to changesin the velocity of the vehicle, comprising the steps of: arranging onthe vehicle at least one audio signal emitting device having aninactivated state and an activated state in which an audio signal isemitted, and controlling the activation of said at least one audiosignal emitting device in relation to the rate of change of velocity ofthe vehicle, said activation controlling step comprising the steps of:measuring an absolute velocity of the vehicle, measuring deceleration ofthe vehicle after a brake pedal of the vehicle is depressed, andactivating said at least one audio signal emitting device from itsinactivated state to its activated state only if the absolute velocityis greater than a threshold velocity and the measured deceleration isgreater than a deceleration threshold.
 23. A method for alerting driversapproaching from a rear of the vehicle to changes in the velocity of thevehicle, comprising the steps of: arranging on the vehicle at least oneaudio signal emitting device having an inactivated state and anactivated state in which an audio signal is emitted, and controlling theactivation of said at least one audio signal emitting device in relationto the absolute velocity of the vehicle, said activation control stepcomprising the steps of: measuring an absolute velocity of the vehicle,measuring deceleration of the vehicle after a brake pedal of the vehicleis depressed, enabling manual activation of said at least one audiosignal emitting device from said inactivated state to said activatedstate if the measured absolute velocity is less than a thresholdvelocity, and automatically activating said at least one audio signalemitting device from its inactivated state to its activated state if theabsolute velocity is greater than the threshold velocity and themeasured deceleration is greater than a deceleration threshold.